CPU goes to 100 deg coming out of standby

Within the past year, I replaced the original drive with a 512 Gb Fusion drive from iFixit. I also replaced the CDROM with an SSD drive. I don't have a reason to believe this is causing my problem but it is worth mentioning.

When I look at my CPU temp with iStat right after coming out of standby, it is 38 C. Within 5 min, if I do nothing, it is up to 100 C, and Heatsink B is 78 C. Fan is maxed out at 6200 RPM. It then settles down to something like 91 C / 75 C. Room is cool and laptop is on a hard surface and well ventilated externally. These numbers are obtained running as a laptop, but the same kind of thing happens in closed-clamshell mode with an external display. In fact, in closed-clamshell mode I have had some "You need to reboot your computer" conditions, which I'm guessing are due to overheating.

Some things to consider (from other postings) seem to be:

1. Run the hardware test.

2. Check for fan obstruction or dirt. (The fan sounds good -- nice, even white noise; not too loud.)

3. Replace heat-sink compound.

Is that the best sequence to try? The disparity between CPU temperature and heat-sink temperature leads me to suspect (3), but I don't know what normal is.

Also, I have about 10 browser tabs normally open in 2 chrome windows, but I have flash disabled. Activity Manager and top show low activity with a load factor of 0.23. It may briefly peak for a few seconds after coming out of standby, but still, I can't connect the high temp to anything I'm doing under these conditions. No vidio streaming, no games, no great CPU or graphical load.

For a while I disabled the kernel_task kext that was taking up CPU, but have re-enabled it and see it running from time to time.

1 Answer

Sounds like you have a SATA I/O issue here. This model has a SATA II (3.0Gb/s) I/O and its possible your SSD and/or HD is SATA III (6.0Gb/s). Make sure both are able to run as the slower SATA II speed.

The fact the indexer was consuming a lot of CPU resource implies the CPU & HD/SSD where struggling getting the read or the write to complete the first time.

Thanks for your response. But how would I "make sure" that the devices are SATA-II-compatible?

I've done a little more investigation.

I have unmounted the SSD drive and the problem continues (but maybe not as badly). So I believe I can rule out the SSD.

On my order, the hybrid drive shows up as:

IF107-098-1 500 GB SSD Hybrid 2.5" Hard Drive

This item is still available with the same part number. The description says it is compatible with "All MacBooks and MacBook Pros (excluding MacBook Air and MacBook Pro Retina)", and this certainly includes the MBP 13", mid-2009.

Also, I do not see a lot of indexing behavior. mds and mdworker are occasionally visible in Activity Monitor, but rarely, if ever, above 4% CPU.

Do you still think it could be a SATA version problem, or if not, do you have any other suggestions?

Nope, classic symptom of a SATA I/O speed issue between the system and the HD and/or SSD. The indexer function causes a lot of I/O on the CPU & HD/SSD so if the drive is too fast it will need to retry the read/write per each block. So the queue is always full with retries which is what pushes the CPU and then the HD/SSD which causes the system to heat up adding more stress.

Though unmounted, the SSD is a model OCZ-VERTEX3 MI. The spec sheet is at http://ocz.com/consumer/download/product... and shows, for Interface, "SATA III / 6Gbps (Backwards compatible with SATA II / 3Gbps, but optimized for SATA 6Gbps) "

Look again on the spec sheet SATA Transfer Rates Supported (Gb/s) - 6.0/3.0/1.5 so your HD is OK here. The only other thing is the SATA cable could be bad. But, were is the HD mounted could be the issue here. Auto sense drives need to be connected to the HD SATA port not the optical drive carrier to work properly.